Pump is the dhcp client on dsl 3/4.pump -i eth0 --statusto get the dhcp info on the eth0 interface.

If udhcpc is being used instead (Busybox dhcp client) then there is no easy way (that I can find). Quickest is to look at what the default gateway is with the "route" command. More often then not, the gateway will also be the dhcp server.